Resiliant Spinal Plate System

ABSTRACT

An embodiment of the invention provides for a system, such as a cervical plate fusion system, that has mechanisms for preventing bone anchors (e.g., screws, pins, and the like) from backing out of the plate. The system prevents both counter-rotation of the screw and axial backing out of the screw. Other embodiments are described herein.

This application is a continuation of U.S. patent application Ser. No.15/917,117, filed Mar. 9, 2018, and entitled “Resiliant Spinal PlateSystem”, which is a continuation of U.S. patent application Ser. No.14/724,323, filed May 28, 2015, and entitled “Resiliant Spinal PlateSystem”, which issued on Mar. 13, 2018, as U.S. Pat. No. 9,913,672,which claims priority to U.S. Provisional Patent Application No.62/003,984 filed on May 28, 2014, and entitled “Resiliant Spinal PlateSystem”. The content of each of the above applications is herebyincorporated by reference.

BACKGROUND

Spinal fixation devices can be used to provide, for example,immobilization and stabilization of spinal segments in patients (e.g.,humans, dogs, cats, and other animals). Fixation devices may be used tohelp fuse bone segments (e.g., vertebrae) in the treatment ofinstabilities or deformities of, for example, the cervical, thoracic,lumbar, and/or sacral spine. Such instabilities or deformities mayinclude, for example, degenerative disc disease (DDD);spondylolisthesis; trauma (i.e., fracture or dislocation); spinalstenosis; curvatures (i.e., scoliosis, kyphosis, and/or lordosis);tumor; pseudoarthrosis; and failed previous fusions.

However, there are risks associated with such fixation devices. Suchrisks include, for example, device component fracture, loss of fixationwhen the device/tissue bond is weakened or lost, non-union, fracture ofthe vertebra, neurological injury, and vascular or visceral injury. Forexample, internal fixation appliances are load sharing devices used toobtain bone alignment until normal healing occurs. Thus, implants aresubjected to loads such as repetitive loads that occur when fixationsystems are subjected to loading associated with, for example, normalpatient movements (e.g., walking and bending), delayed union, ornon-union situations. These loads can cause screws, which couple afixation plate to bone, to loosen. The screws may loosen by, forexample, backing out. This “backing out” may occur due to unwanted screwrotation (e.g., when the screw rotates and “unscrews” from the bone)and/or unwanted screw axial movement that is directed away from thebone. The axial movement may or may not be caused by the unwanted screwrotation. When a screw or screws back out and away from the plate andbone, the plate may become unstable and lead to complications for thepatient. The degree or success of union, loads produced by weightbearing, and activity levels will, among other conditions, dictate thelongevity of the implant. Robust fixation systems are needed to lessenrisks associated with fixation and to promote better outcomes forpatients.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the present invention willbecome apparent from the appended claims, the following detaileddescription of one or more example embodiments, and the correspondingfigures, in which:

FIGS. 1-16 include different perspectives of a plate and resilientretaining member in embodiments of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. Well-known structures andtechniques have not been shown in detail to avoid obscuring anunderstanding of this description. References to “one embodiment”, “anembodiment”, “example embodiment”, “various embodiments” and the likeindicate the embodiment(s) so described may include particular features,structures, or characteristics, but not every embodiment necessarilyincludes the particular features, structures, or characteristics.Further, some embodiments may have some, all, or none of the featuresdescribed for other embodiments. Also, as used herein “first”, “second”,“third” and the like describe a common object and indicate thatdifferent instances of like objects are being referred to. Suchadjectives are not intended to imply the objects so described must be ina given sequence, either temporally, spatially, in ranking, or in anyother manner. Also, the terms “coupled” and “connected,” along withtheir derivatives, may be used. In particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalcontact with each other and “coupled” may mean that two or more elementsco-operate or interact with each other, but they may or may not be indirect physical contact.

An embodiment of the invention provides for a system, such as a cervicalplate fusion system, that has mechanisms for preventing bone anchors(e.g., screws, pins, and the like) from backing out of the plate. Thesystem prevents both counter-rotation of the screw and axial backing outof the screw. Other embodiments are described herein.

FIGS. 1-16 include plate 100. Plate 100 may be used for fusion ofcervical vertebrae but may also be used for fusion of other vertebrae(e.g., thoracic, lumbar) or for fixation of other tissues (e.g.,adjacent bone sections of a femur or other bone or tissue) and the like.

In FIG. 1, plate 100 includes apertures 101, 102, 103, 104, 105, 106.These apertures or holes may have continuous perimeters but may alsoinclude discontinuous perimeters that do not form a complete circle,oval, rectangle and the like. The apertures (e.g., holes) need not becircular, symmetrical, or have any one particular perimeter, even thoughapertures 101, 102, 103, 104, 105, 106 each include a generallycontinuous circular perimeter. The three pairs of holes (101 and 104,102 and 105, 103 and 106) of plate 100 are for a two level fusion systemwhere two vertebral discs are to be fused. For example, only holes 101,102, 104, 105 would be needed for a one level fusion. A fourth pair ofholes may be needed for a three level fusion.

In FIG. 12, plate 100 includes cavities 110, 111, 112. These cavitiesare provided for each of apertures 101, 102, 103, 104, 105, 106. In FIG.16, a single-piece monolithic resilient member 125 includes projections120, 121, 122 that respectively fit within cavities 110, 111, 112.During manufacturing member 125 may be formed in the “horseshoe” patternshown in FIG. 16. The member may be formed as a single monolithicelement with no weldings or fixtures used to assemble member 125. InFIGS. 6 and 7, screw 132 includes lip 131, which is coupled to an angledor beveled shoulder 133, and a toothed wheel 134 having teeth such astooth 138 and tooth 139.

A method addresses various embodiments of the invention. For example, auser inserts screw 132 into hole 102 of plate 100. Cavities 110, 111,112 respectively include portions 120, 121, 122 of resilient member 125.Fins or projections 120, 122 respectively project into hole 102. Thus,at least a portion of fins 120, 122 project into hole 102.

In an embodiment, resilient member 125 is seperably coupled to plate100. For example, during assembly (e.g., at a manufacturing plant, in anoperating room, in a medical office, etc.) member 125 may be compressedand then inserted into cavity 113, which includes channels 110, 111,112. In an embodiment, member 125 is retained within cavity 113 (shownwith portions of plate 100 cut away in FIG. 13 to better show cavity113) based on a resistance fit where member 125 does not require use ofa weld, screw, clamp, or the like to hold member 125 within cavity 113.Consequently, member 125 has advantages related to ease of manufacturingand also related to ease of assembly into plate 100. Placing member 125within (partially or fully) cavity 113 helps reduce the overall profileof the plate system, thus providing a less intrusive system for thepatient.

As seen in FIG. 6, fin 122 has an angled leading edge 123 and a trailingedge 124, leading edge 123 being non-orthogonally connected to arm 127.As seen in FIG. 16, fin 120 has an angled leading edge 123′non-orthogonally connected to arm 126. Regarding the screw thatinterfaces member 125, FIG. 6 shows how tooth 137 has angled leadingedge 136 and curved trailing edge 135. Fin 122 is sized to be receivedbetween teeth 137, 137′ of toothed wheel 134.

FIG. 7 depicts an embodiment of the invention with a screw inserted intoa hole.

Returning to the method, shoulder 133 of screw 132 deflects member 125.Specifically, when screw 132 is in a partially implanted position and isbeing inserted into hole 102 beveled shoulder 133 is actively deflectingfins 120 and/or 122 medially or laterally respectively.

As the method continues the user advances screw 132 into a fullyimplanted position such that screw 132 is prevented from backing out ofhole 102 by fin 120 and/or 122. At this point fin 120 and/or 122 hassnapped back towards the center of aperture 102 after having beendeflected (medially (if fin 120) or laterally (if fin 122)) respectivelyinto channels 110, 112 to now intercept lip 131 if and when screw 132“backs out” or travels (or attempts to “back out” or travel) axiallyaway from patient bone in which it is implanted. Also, while toothedwheel 134 is allowed to rotate in one direction (e.g., clockwise totighten screw 134 into bone) toothed wheel 134 is prevented fromcounter-rotating (e.g., counter clockwise to loosen and “back out” frombone) because trailing edge 124 of fin 122 is lodged against trailingedge 135 of tooth 137. In FIG. 7, members 120 and 122 have both “snappedback” towards the middle of hole 102.

In FIG. 1, plate 100 includes viewing apertures 107, 108 which allowpatient tissue to be viewed by a user upon implantation of the systeminto a patient. Bone tissue may be inserted through apertures 107, 108to facilitate fusion. As seen in FIG. 1, no resilient member (e.g.,member 125) projects into either of apertures 107, 108. Also, cavity 113does not connect to either of apertures 107, 108.

In an embodiment, member 125 includes nitonol. However, in otherembodiments member 125 includes other materials such as stainless steeland the like. In an embodiment, member 125 includes a “horseshoe” shapedprofile but may include other shaped profiles (e.g., a bracket, such asa structure similar to an American football field goal having one or twosupport members that couple to a “U” or bracket shaped portion havingtwo arms extending away from the one or to two support members) in otherembodiments.

In an embodiment, screw 132 includes tooth 138, which has a height sizedso when the screw is fully implanted (e.g., with shoulder 133 directlyagainst bone) fin 120 will always be in contact with a portion of tooth138. In other words, in an embodiment fin 109 projects medially out from“T” channel 421 (FIG. 4). If the tooth height is too small, fin 120could spring or project over tooth 138 and possibly loose contact withtooth 138. In such a case screw 132 may begin working loose when not inconstant contact with a tooth included on the toothed wheel becausethere would be no immediate barrier to axial “back out” movement and/orloosening counter-rotation. However, such a scenario may be mitigated oreliminated by properly sizing the tooth height so when the screw isfully implanted fin 120 will always be in contact with a portion oftooth 138.

In an embodiment, a horizontal axis 199 intercepts first and second finsof 120′, 120″ two resilient members (e.g., medial fins of resilientmembers in a pair of apertures such as apertures 101, 104), does notintercept a lateral wall portion 198 of hole 101, does intercept amedial wall portion 197 of hole 101, and does not intercept fins 122′,122″. Thus curvature of the plate provides for proper lordosis and canbe seen in FIGS. 10-11. Also, the horizontal axis intercepts the firstand second medial fins of a single level (e.g., medial fins of resilientmembers 125 in apertures 101, 104). The design of the system allows forscaling between various embodiments that correspond to varying fusionlevels whereby different embodiments suited for different levels offusion use different numbers of identical resilient members, regardlessof where the resilient members are located in the plates.

In various embodiments screw 132 includes an overall height (proximalend or head to distal end or tow) of generally 1.2, 1.3, 1.4, 1.5, 1.6,1.7, or 1.8 mm.

In various embodiments, a plate may forego use of a cavity (thatcorresponds to a resilient member) and may instead couple the resilientmember to an outer surface of the plate. The resilient member may alsobe integral or monolithic with the plate. Also, fins may include variousgeometries and may include, for example, orthogonal dimensions such thatthe fin has straight edges that fit at right angles to an arm ofresilient member. The fin may be rectangular, square, and the like. Thesame may be the case for teeth on the screw such that the teeth may havestraight edges that fit at right angles to the toothed wheel.

Also, embodiments do not necessarily require that the screw include a“highly” toothed wheel but may also include a screw with a few (e.g.,one or two) simple projections that serve as teeth to accomplish thegoal of preventing unwanted rotation. Also, while “rotation” and“counter rotation” have been used herein those terms should not beassumed to be associated with, for example, any particular directionsuch as “clockwise” for “rotation” or “counter clockwise” for “counterrotation.” Also, screws may include lips that are not necessarilylimited to flanges and the like. Lips may include floors or basicimpediments to, for example, vertical or axial movement away from bone.

Embodiments described herein have many advantages.

First, in an embodiment projection 121 fits within aperture 111 therebypreventing rotation of member 125 within channel 113. Thus, member 125is securely fitted within slot 113 even if only by resistance fit(although portions of member 125 may be coupled to plate 100 usingwelds, adhesives, and the like in other embodiments).

Second, in an embodiment member 125 provides two fins 120, 122 to engagesurface 131 of screw 132. This is in contrast to conventional systemsthat may provide only a single fin or surface for engaging a screw andpreventing back out by the screw. This can be a critical issueconsidering screw 132 is not always implanted straight into a bone butmay instead be offset towards direction 140 (FIG. 7), which would causesurface 131 to rotate towards fin 120 but away from fin 122.Furthermore, screw 132 may be offset towards direction 141, which wouldcause surface 131 to rotate towards fin 122 but away from fin 120. Thisprevents the screw head from working past all the fins of a systembecause even if one of the fins (120, 122) is not in contact or in lineto stop screw 132 from backing out, the other of the fins (120, 122)will be in contact or in line to stop screw 132 from backing out. If aconventional system were to only have a single projection, such assomething roughly analogous to fin 120, offset of screw 132 alongdirection 141 may cause surface 131 to be able to back out past theportion analogous to fin 120 (or even if screw 132 does not blackoutpast the portion analogous to fin 120, there may be a lack of stabilityif nothing analogous to fin 122 is present).

Third, in an embodiment fins 120, 122 are 180 degrees from one another.In such a scenario screw 132 may be offset towards direction 142 (out ofthe page for FIG. 7), but doing so would not cause surface 131 to rotateaway from either of fins 120, 122 (but instead merely pivot about fins120, 122). In such a scenario screw 132 may be offset towards direction143 (into the page for FIG. 7), but doing so would not cause surface 131to rotate away from either of fins 120, 122 (but instead merely pivotabout fins 120, 122).

Fourth, anti-rotation member 121 may be formed parallel to a long mainaxis 191 that bisects graft windows 107, 108 (see FIGS. 1 and 8). Byforming member 121 in this location an embodiment may allow for athinner sidewall portion 190 (as measured orthogonal to the long axis191). In an embodiment the sum of the widths (as measured orthogonal tothe long axis 191) of portions 190, 192 is less than the width of middleportion 193. This creates a smaller profile which can be desirable forthe patient. For example, in FIG. 9 the sum of distances 194, 195 may beless than distance 196.

While four specific advantages are addressed immediately above, notevery embodiment requires each of those four advantages. For example,member 121 may be unnecessary in some embodiments if slot 113 is also ina horseshoe pattern and does not allow for rotation of the resilientmember. Further, some embodiments do not necessarily place fins 180degrees from each other but may instead place them 170, 160, 145, 130,120, 110, 90, 70, 60, 40 degrees from one another.

An embodiment includes an orthopedic fusion system comprising: a platethat includes a first aperture; a single-piece monolithic resilientmember included in a first cavity that directly contacts the firstaperture, the resilient member including a first arm connected to afirst end having a first fin and a second arm connected to a second endhaving a second fin; a screw including a lip, which is coupled to abeveled shoulder, and a toothed wheel having first and second teeth;wherein (a) the resilient member is seperably coupled to the plate andwithin the first cavity; (b) the first cavity includes first and secondchannels that respectively include first and second portions of thefirst and second ends; (c) the first and second fins respectivelyproject into the first aperture; (d) the first fin has a first angledleading edge and a first curved trailing edge, the first angled leadingedge of the first fin being non-orthogonally connected to the first arm;(e) the first tooth has a first angled leading edge and a first curvedtrailing edge, the first angled leading edge of the first tooth beingnon-orthogonal to a tangent intersecting the toothed wheel at a pointwhere the first angled leading edge of the first tooth intersects thetoothed wheel; and (f) the first fin is sized to be received between thefirst and second teeth of the toothed wheel; wherein the system isconfigured such that (g) in a partially implanted position the screw isinserted into the first aperture and the beveled shoulder is activelydeflecting the first fin medially and the second fin laterally; and (h)in a fully implanted position (1) the screw is inserted into the firstaperture such that the screw is prevented from backing out of the firsthole by the first and second fins that have snapped back into the firstaperture to intercept the lip when the screws travels axially away frompatient bone in which it is implanted and (2) the toothed wheel isallowed to rotate but is prevented from counter-rotating because thefirst curved trailing edge of the first fin is lodged against the firsttrailing edge of the first tooth.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. An orthopedic fusion system comprising: a platethat includes a first aperture; a single-piece monolithic resilientmember included in a first cavity that directly contacts the firstaperture, the resilient member including a first arm connected to afirst end having a first fin and a second arm connected to a second endhaving a second fin; and a screw including a lip, which is coupled to abeveled shoulder, and a toothed wheel having first and second teeth;wherein (a) the resilient member is seperably coupled to the plate andwithin the first cavity; (b) the first cavity includes first and secondchannels that respectively include first and second portions of thefirst and second ends; (c) the first and second fins respectivelyproject into the first aperture; (d) the first fin has a first angledleading edge and a first trailing edge, the first angled leading edge ofthe first fin being non-orthogonally connected to the first arm; (e) thefirst tooth has a first angled leading edge and a first trailing edge,the first angled leading edge of the first tooth being non-orthogonal toa radius from a tip of the first angled leading edge of the first toothto a long axis of the screw; and (f) the first fin is sized to bereceived between the first and second teeth of the toothed wheel;wherein the system is configured such that (g) in a partially implantedposition the screw is inserted into the first aperture and the beveledshoulder is actively deflecting the first fin medially and the secondfin laterally; and (h) in a fully implanted position (1) the screw isinserted into the first aperture such that the screw is prevented frombacking out of the first aperture by the first and second fins that havesnapped back into the first aperture to intercept the lip when thescrews travels axially away from patient bone in which it is implanted,and (2) the toothed wheel is allowed to rotate but is prevented fromcounter-rotating because the first trailing edge of the first fin islodged against the first trailing edge of the first tooth.